The overall objective of this proposal is to define the immunoregulatory role of anti-idiotypic antibodies to anti-HLA. Using a microcytotoxicity inhibition assay, we have recently obtained evidence for development of anti-HLA antibodies followed by anti-idiotypic antibodies to HLA class 1 and 11 antibodies in human liver allograft recipients. The proposed research will define the fine specificities of anti-anti-HLA activity using multiple monospecific anti-HLA reagents in order to determine the extent of idiotypic cross-reactivity that exists between antibodies that define distinct polymorphisms of MHC class 1 and class 11 antigens. In particular, these studies will define the extent to which antibodies directed to cross-reactive HLA epitopes (CREGs) express cross-reactive idiotopes. Our preliminary studies Indicate that these anti-idiotypic antibodies to anti-HLA antibodies bind to autologous stimulated T cell and possibly to the clonotypic T cell structures. We will determine the ability of pre- and post- transplant sera to bind to autologous normal and activated T lymphocytes, including biopsy derived T cell clones, using immunofluorescence and flow cytometry. We will use selected sera which bind to T cells in immunoprecipitation analysis, to define the immunochemical nature of the membrane molecules reactive to the anti-idiotypic antibodies. Since anti-idiotypic antibodies to anti-HLA antibodies are reactive with T cells possibly via T cell clonotypic structures, we will determine the immunoregulatory effects of these antibodies on specific cellular immune functions. We will analyze the capacity of anti-idiotypic antibodies to block mixed lymphocyte culture responses of recipients against donor antigens, to block cytotoxic T lymphocyte generation and killing, and to Inhibit proliferation and/or killing by biopsy derived cloned T lymphocytes. Finally, we will develop methods with which to establish anti-anti-HLA secreting B cells; these will include transformation of B cells secreting antibodies using Epstein-Barr virus and/or fusion with mouse myeloma partners. The long term goal of this study is to further define the role of anti-idiotypic antibodies in the regulation of human immune responses so that idiotypic manipulation of immune response to transplantation and tumor antigens can become a viable goal.